Symfony version(s) affected: 3.4 until master

Description
In one of my apps I process messages from AMQP asynchronously using a Symfony command worker (not using symfony/messenger).
Every message is handled in a fresh newly booted kernel to ensure proper isolation.

This worked fine until recently through some changes in our app the session service is used (instantiated & started) during the processing of a message.

Whenever within the same php process now another message gets handled (with a new kernel) we get the following error:

"Warning: ini_set(): A session is active. You cannot change the session module's ini settings at this time"

This is because the NativeFileSessionHandler tries to set some ini settings again:
https://github.com/symfony/symfony/blob/master/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/NativeFileSessionHandler.php#L52

And the session from the previous kernel was never closed.

Possible Solution
I discussed this briefly with @nicolas-grekas and to fix this I added the kernel.reset tag to the session service so it can be properly reset. This fixes the issue in my app if I call ServicesResetter::reset() on every kernel before its shut down.